The effect of alumina addition on the conductivity, microstructure and mechanical strength of zirconia — yttria electrolytes

Abstract

Abstract. The effect of alumina additions on the ionic conductivity and mechanical properties of 3 and 8 mol% Y203-ZrO 2 compositions has been investigated. Such materials are of interest for use in fuel cells and other similar applications. Sintered specimens were characterised by XRD, SEM, impedance spectroscopy, four -probe DC conductivity and mechanical strength measurements. Alumina additions had no affect on the conductivity degradation behaviour at 1000 ~ and the activation energy but resulted in an increase in the strength of 8 mol% Y203 -ZrO2 composition by about 25%. However, a significant drop in the ionic conductivity well above what could be accounted for by the decrease in the volume fraction of the conducting phase, was observed.

Oxygen-ion conducting electrolyte materials for solid oxide fuel cells

“…Similarly a large reduction in the conductivity, as a result of alumina addition, was reported for ZrO2 -Y203 and ZrO2 -Sc203 systems by Badwal et al [18,29]. This is attributed in part to a decrease in the volume fraction of the conducting phase and in part to the additional constriction provided by alumina grains present at grain boundaries or in the bulk of the grain to migrating oxygen-ions [22,29,61]. Alumina remains mainly an inert phase in the electrolyte matrix.…”

“…The addition of up to 1 -2 wt% A1203 has very little effect on the mechanical strength, but several reports indicate some beneficial effect on the total conductivity of the material [67,68]. However, for larger additions of alumina, the conductivity reduction is much higher than that can be accounted for by an increase in the volume fraction of alumina [ 18,22,29,61]. Yamamoto et al [22], in the case of ZrO 2 -5c203 -A1203 system, reported a reduction in the conductivity by a factor of about two by the mere addition of 20 wt% alumina to 11 mol% Sc203 -ZrO 2.…”

“…The reason for this may be related to * Conductivity values from references [18], [19], [29], [40] are initial values in as-sintered materials recorded without ageing at the stated temperatures. The degradation occurs in most ZrO 2 -Y203 and ZrO 2 -Sc20 3 materials as discussed in section 2.6. similar ionic radius for both Zr 4+ and Sc 3+ cations.…”

Effect Of The Gadolinium Oxide Addition On The Electrical Properties Of Tetragonal Zirconium Dioxide

“…its mechanical strength exceeds ca. twice the mechanical strength of the cubic phase zirconia [17]. At moderate temperatures below 700…”

“…Basing on literature data [17,18] as well as own studies [19] tetragonal zirconia: ZrO 2 +3 mol % Y 2 O 3 (3YSZ) can be promising solid electrolyte in IT-SOFC. Tetragonal zirconia shows excellent mechanical properties, i.e.…”